Polishing pad comprising magnetically sensitive particles and method for the use thereof

ABSTRACT

The invention provides polishing pads comprising a deformable polishing pad body and magnetically sensitive particles dispersed therein, wherein one or more properties of the polishing pad are altered when in the presence of an applied magnetic field. The invention further provides a polishing system and a method for polishing a substrate involving such a polishing pad.

FIELD OF THE INVENTION

This invention pertains to a polishing pad that is useful forchemical-mechanical polishing.

BACKGROUND OF THE INVENTION

Chemical-mechanical polishing (“CMP”) processes are used in themanufacturing of microelectronic devices to form flat surfaces onsemiconductor wafers, integrated circuits, field emission displays, andmany other microelectronic substrates. For example, the manufacture ofsemiconductor devices generally involves the formation of variousprocess layers, selective removal or patterning of portions of thoselayers, and deposition of yet additional process layers above thesurface of a semiconducting substrate to form an integrated circuit. Theprocess layers can include, by way of example, insulation layers, gateoxide layers, conductive layers, and layers of metal or glass, etc. Itis generally desirable in certain steps of the process that theuppermost surface of the process layers be planar, i.e., flat, for thedeposition of subsequent layers. CMP is used to planarize process layerswherein a deposited material, such as a conductive or insulatingmaterial, is polished to planarize the wafer for subsequent processsteps.

In a typical CMP process, a wafer is mounted upside down on a carrier ina CMP tool. A force pushes the carrier and the wafer downward toward apolishing pad. The carrier and the wafer are rotated above the rotatingpolishing pad on the CMP tool's polishing table. A polishing composition(also referred to as a polishing slurry) generally is introduced betweenthe rotating wafer and the rotating polishing pad during the polishingprocess. The polishing composition typically contains a chemical thatinteracts with or dissolves portions of the uppermost wafer layer(s) andan abrasive material that physically removes portions of the layer(s).The wafer and the polishing pad can be rotated in the same direction orin opposite directions, whichever is desirable for the particularpolishing process being carried out. The carrier can also oscillateacross the polishing pad on the polishing table.

Polishing pads used in chemical-mechanical polishing processes aremanufactured using both soft and rigid pad materials, which includepolymer-impregnated fabrics, microporous films, cellular polymer foams,non-porous polymer sheets, and sintered thermoplastic particles. A padcontaining a polyurethane resin impregnated into a polyester non-wovenfabric is illustrative of a polymer-impregnated fabric polishing pad.

Despite the attention that has been directed towards improvement ofpolishing pads for CMP, the polishing pads are typically fixed elementsin the CMP process. That is, once a polishing pad has been selected andplaced into use, the physical characteristics of the polishing padcannot be altered during the course of chemical-mechanical polishingoperations. However, the surface characteristics of the polishingsubstrate undergo changes as the surface is polished and approachesplanarity. Consequently, there remains a need for a polishing pad, apolishing system, and a polishing method that allows for control of thepolishing pad characteristics during the polishing operation.

The invention provides such a polishing pad, system, and method. Theseand other advantages of the invention, as well as additional inventivefeatures, will be apparent from the description of the inventionprovided herein.

BRIEF SUMMARY OF THE INVENTION

The invention provides a polishing pad comprising a deformable polishingpad body and magnetically sensitive particles dispersed therein, whereinone or more properties of the polishing pad are altered when in thepresence of an applied magnetic field. The invention also provides apolishing system comprising (a) a polishing pad comprising a deformablepolishing pad body and magnetically sensitive particles dispersedtherein, wherein one or more properties of the polishing pad are alteredwhen in the presence of an applied magnetic field, and (b) anadjustable-strength magnetic field positioned proximate to the polishingpad. The invention further provides a method of polishing a substratecomprising (a) providing a polishing pad comprising a deformablepolishing pad body and magnetically sensitive particles dispersedtherein, wherein one or more properties of the polishing pad are alteredwhen in the presence of an applied magnetic field, (b) contacting thepolishing pad with a substrate, (c) applying a magnetic field to thepolishing pad, and (d) moving the polishing pad relative to thesubstrate, thereby polishing the substrate.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a polishing pad comprising a deformable polishingpad body and magnetically sensitive particles dispersed therein, whereinone or more properties of the polishing pad are altered when in thepresence of an applied magnetic field. When a magnetic field is appliedto the polishing pad of the invention, the magnetically sensitiveparticles contained within the deformable polishing pad body arerepulsed by or attracted to the magnetic field and exert a force uponthe deformable polishing pad body. This force causes the polishing padbody to deform (e.g., expand or contract in one or more dimensions),which alters one or more properties of the polishing pad comprising thedeformable polishing pad body. The polishing pad of the invention, thus,allows a user to customize the properties of the polishing pad duringuse by applying a magnetic field to the polishing pad.

The term “applied magnetic field,” as used herein, refers to a magneticfield applied to the polishing pad of the invention in addition to anynatural magnetic field (e.g., the earth's magnetic field) that may bepresent at the particular location in which the polishing pad is used.The term “magnetically sensitive particles,” as used herein, refers toany particle that is attracted to, or repulsed by, the applied magneticfield.

The magnetically sensitive particles can comprise inorganic particles,organic particles, or a mixture of inorganic and organic particles.Inorganic magnetically sensitive particles are well known in the art,and include Fe₃O₄, Nd—Fe—B, Ba—Sr ferrite, Ni—Zn—Cu ferrite, SmCo₅,Sm₂Co₁₇, iron, steel, and mixtures thereof. Organic (or metal-organic)magnetically sensitive particles useful in accordance with the presentinvention include those described in “Metal-Organic and OrganicMolecular Magnets”, editors P. Day and A. F. Underhill (The RoyalSociety of Chemistry, Cambridge, 1999) and “Organic Conductors,Superconductors and Magnets: From Synthesis to Molecular Electronics”,editors Lahcene Ouahab and Eduard Yagubskii (Kluwer Academic Publishers,2004). Preferably, the organic or metal-organic particles are selectedfrom the group consisting of V[tetracyanoethylene]_(˜2),V[Cr(CN)]_(˜0.9), Cr(tetracyanoethylene)₂, KV[Cr(CN)₆], and C-60fullerene, any of which can further comprise molecules of salvationdepending upon the method of synthesis (e.g., V[Cr(CN)]_(˜0.9).2.8H₂O,KV[Cr(CN)₆].2H₂O, and the like).

While the magnetically sensitive particles may be used without anyparticular treatment, in some instances it may be desirable to coat theparticles, for example, to improve the dispersibility or adherence ofthe magnetically sensitive particles in the material of the deformablepolishing pad. Any suitable coating can be used provided that thecoating does not substantially interfere with or eliminate the magneticsensitivity of the particles. Useful coatings include polymer coatings,such as coatings comprising polyurethane, nylon, polyethylene, or anyother polymer that imparts a desired property to the particles.

The deformable polishing pad body can comprise any suitable amount ofmagnetically sensitive particles. The amount of magnetically sensitiveparticles will affect the degree to which the deformable polishing padbody responds to an applied magnetic field. Increasing the amount ofmagnetically sensitive particles will typically increase the degree towhich the deformable polishing pad body deforms in the presence of anapplied magnetic field and, thereby, increase the degree to which theproperties of the polishing pad are altered. Decreasing the amount ofmagnetically sensitive particles generally has the opposite effect. Theinventive polishing pad can comprise about 0.1 wt. % or more (e.g.,about 5 wt. % or more, or about 10 wt. % or more) of the magneticallysensitive particles, such as about 20 wt. % or more (e.g., about 30 wt.% or more), or about 40 wt. % or more (e.g., about 60 wt % or more) ofthe magnetically sensitive particles. Typically, the inventive polishingpad will comprise about 60 wt % or less of the magnetically sensitiveparticles, and can comprise about 40 wt. % or less, such as about 20 wt.% or less (e.g., about 10 wt % or less, or about 5 wt % or less) of themagnetically sensitive particles.

The magnetically sensitive particles can have any suitable averageparticle diameter. As used herein, the term “average particle diameter”refers to the average diameter on a number basis. Typically, themagnetically sensitive particles have an average particle diameter ofabout 5 μm or less, such as about 3 μm or less, or even about 1 μm orless. The average particle diameter of the magnetically sensitiveparticles is generally within the range of about 0.1 to about 5 μm, suchas about 0.3 to about 3 μm, or even about 0.5 to about 1 μm. Themagnetically sensitive particles can have any suitable shape includingspheres, rectangular solids, cubes, flakes, acicular shapes, andmixtures thereof.

The deformable polishing pad body comprising the magnetically sensitiveparticles can be made from any suitable material provided that it allowsthe properties of the polishing pad to be altered when a magnetic fieldis applied as compared to the properties of the polishing pad in theabsence of the magnetic field. The effect of an applied magnetic fieldon the properties of the polishing pad will, of course, depend not onlyupon the material of the polishing pad, but also upon the concentrationof magnetically sensitive particles present in the polishing pad and thestrength of the applied magnetic field. Accordingly, the choice of theparticular material used will depend upon the particular padconfiguration and the desired application.

In general, the deformable polishing pad body will comprise anelastomeric material, such as a natural or synthetic elastomericpolymer. Suitable polymers include elastomers, polyurethanes,polyolefins, polycarbonates, polyvinylalcohols, nylons, natural andsynthetic rubbers, styrenic polymers, polyaromatics, fluoropolymers,polyimides, cross-linked polyurethanes, thermoset polyurethanes,cross-linked polyolefins, polyethers, polyesters, polyacrylates,elastomeric polyethylenes, copolymers and block copolymers thereof, andmixtures and blends thereof.

The polishing pad comprising the deformable polishing pad body andmagnetically sensitive particles can have any suitable storage modulus.In the absence of an applied magnetic field, the storage modulus of thepolishing pad typically will be about 100-1000 MPa, such as about400-900 MPa or even about 450-800 MPa (e.g. about 500-700 MPa). Thepolishing pad can be configured with a lower storage modulus, as may beappropriate for certain applications. Thus, the polishing pad of theinvention can have a storage modulus of 350 MPa or less (e.g., about 0.1MPa to about 350 MPa, such as about 1 MPa to about 350 MPa, or about 10MPa to about 350 MPa, or even about 100 MPa to about 350 MPa). Thestorage modulus of the polishing pad can be determined according to theprotocol reported in ASTM D790.

The polishing pad comprising the deformable polishing pad body andmagnetically sensitive particles can have any suitable compressibility.The compressibility is generally stated as a percent-change in thethickness of the polishing pad under a given load (e.g., the thicknessof the polishing pad under a given load over the original polishing padthickness (no load) stated as a percent). A preferred method fordetermining the compressibility of the polishing pad comprises: (a)determining the thickness of the polishing pad without any load applied(D1), (b) applying a given load (e.g., about 32 kPa (about 4.7 psi)) tothe polishing pad for about one minute to compress the polishing pad,(c) determining the thickness of the compressed polishing pad (D2), and(d) determining the percent-compressibility according to the followingrelationship:percent-compressibility(%)=[(D1−D2)/D1]×100.The compressibility of the polishing pad can be determined with theassistance of commercially available instruments (e.g., “Ames Meter”model BG2500-1-04 manufactured by B.C. Ames Inc.). In the absence of anapplied magnetic field, the average percent compressibility of thepolishing pad under a load of about 32 kPa will generally be about 2% ormore, such as about 4% or more, or even about 10% or more (e.g., about15% or more, or even about 20% or more). The compressibility willgenerally be within the range of about 2-50%, such as about 4-40%, orabout 10-30%.

The polishing pad comprising the deformable polishing pad body andmagnetically sensitive particles can have any suitable resilience.Resilience is typically recited as percent-rebound capacity. A preferredmethod for determining the percent-rebound capacity of a polishing padcomprises: (a) determining the thickness of the polishing pad withoutany load applied (D1), (b) applying a given load (e.g., about 32 kPa(about 4.7 psi)) to the polishing pad for about one minute to compressthe polishing pad, (c) determining the thickness of the compressedpolishing pad (D2), (d) removing the load from the polishing pad andallowing the polishing pad to rebound for about one minute, (e)determining the thickness of the rebounded polishing pad (D3), and (f)determining the percent-rebound capacity of the polishing pad accordingto the following relationship:percent-rebound(%)=[(D3−D2)/(D1−D2)]×100.As with compressibility, the percent-rebound of the polishing pad can bedetermined with the assistance of commercially available instruments,such as the aforementioned “Ames Meter.” For most applications, it isdesirable that the polishing pad has a high percent-rebound capacity inthe absence of an applied magnetic field. Thus, the polishing padpreferably has a percent-rebound capacity, after application of a loadof about 32 kPa (about 4.7 psi), of about 50% or more, such as about 60%or more, or even about 85% or more. Of course, lower percent-reboundcapacities of about 25% or more (e.g., about 30% or more, or about 40%or more) may be suitable for some applications.

The polishing pad comprising the deformable polishing pad body andmagnetically sensitive particles can have any suitable hardness.Hardness can be measured according to the Shore method using adurometer, for example, according to ASTM D-2240-95. Thus, the polishingpad of the invention can have a Shore hardness of about 40 A to about 90D. Generally, the Shore hardness of the polishing pad in the absence ofan applied magnetic field will be about 90 D or less, such as about 70 Dor less, or even about 50 D or less (wherein the “D” designationrepresents the hardness on the Shore “D” scale), and will be within therange of about 40 D-90 D, such as about 50 D-80 D. For applications inwhich softer polishing pads are needed, the polishing pad of theinvention can be configured with a Shore hardness of about 40 A or more(e.g., about 40 A to about 90 A) or about 60 A or more (e.g., about 60 Ato about 90 A) or even about 70 A or more (e.g., about 70 A to about 90A).

The polishing pad comprising the deformable polishing pad body andmagnetically sensitive particles can be produced by any suitable method.Many such methods are known in the art. Suitable methods includecasting, cutting, reaction injection molding, injection blow molding,compression molding, sintering, thermoforming, or pressing the chosenmaterial into a desired shape. The polymer typically is a pre-formedpolymer; however, the polymer also can be formed in situ according toany suitable method, many of which are known in the art (see, forexample, Szycher's Handbook of Polyurethanes CRC Press: New York, 1999,Chapter 3). For example, thermoplastic polyurethane can be formed insitu by reaction of urethane prepolymers, such as isocyanate,di-isocyanate, and tri-isocyanate prepolymers, with a prepolymercontaining an isocyanate-reactive moiety. Suitable isocyanate-reactivemoieties include amines and polyols. Foam polymers, such as polyurethanefoam polymers, comprising primarily open-cells or closed-cells, or amixture of open and closed cells, also can be used. Techniques for theuse of foam polymers are described in the art and include the mucellprocess, phase inversion process, spinodal or bimodal decompositionprocess, and pressurized gas injection process. Preferably, thepolishing pads are produced using a mucell process or a pressurized gasinjection process.

The polishing pad and deformable polishing pad body comprising themagnetically sensitive particles can have any suitable shape. Typically,the polishing pad and deformable polishing pad body will have the shapeof a belt, a disc or a flat polygonal solid shape (e.g., rectangularsolid) comprising two broad surfaces providing front and rear “faces”and one or more edge surfaces on the perimeter of the polishing pad anddeformable polishing pad body. When used in an apparatus that rotatesthe polishing pad and deformable polishing pad body, the polishing padand deformable polishing pad body will have an axis of rotationperpendicular to the faces.

The magnetically sensitive particles are generally distributed in thematerial of the deformable polishing pad body during the production ofthe pad. The distribution of the magnetically sensitive particles can beeffected in any suitable manner. For example, the magnetically sensitiveparticles can be combined with the material of the deformable polishingpad by mixing or blending prior to forming the material into the desiredshape.

The magnetically sensitive particles can be distributed in the materialof the deformable polishing pad body evenly to provide a uniformdistribution of magnetically sensitive particles, or they can bedistributed in a non-uniform manner. For example, the magneticallysensitive particles can be concentrated in a particular thickness of thedeformable polishing pad body, such as at or near one or both faces ofthe deformable polishing pad, or at the center of the thickness of thedeformable polishing pad body. The magnetically sensitive particles canalso be concentrated at one or more distances from the axis of rotationof the deformable polishing pad body, such as at or near the perimeterof the deformable polishing pad body, or closer to the axis of rotation.Alternatively, the magnetically sensitive particles can be distributedin selected areas of the polishing pad. Preferably, the magneticallysensitive particles are distributed in the polishing pad in a mannerthat reduces the edge effect during polishing (e.g., reduces thetendency of the edges of a substrate to polish at a different rate fromthe rest of the substrate).

When distributed in a non-uniform manner, the magnetically sensitiveparticles can be distributed in distinct concentrated areas, or can bedistributed along a concentration gradient. For example, themagnetically sensitive particles can be present in highest concentrationat the perimeter of the deformable polishing pad body with a decreasingconcentration gradient towards the axis of rotation, or vice versa(e.g., the concentration being highest at the center of the pad anddecreasing towards the axis of rotation). The same types of gradientscan be established through the thickness of the pad as well. Forexample, concentrations of magnetic particles can be highest at thefaces and decrease towards the center thickness, or vice versa.Alternatively, the concentration of magnetic particles can steadilyincrease or decrease from one face to the opposite face. The gradientsof magnetically sensitive particle concentration in the deformablepolishing pad body can be linear or non-linear.

A non-uniform distribution of the magnetically sensitive particles inthe deformable polishing pad body can be accomplished by any suitablemethod. For example, the settling properties of different types or sizesof magnetically sensitive particles can be used to establishconcentration gradients in the material of the deformable polishing padprior to formation. Also, the deformable polishing pad body can beformed using layers or sections having different concentrations ofmagnetically sensitive particles. Alternatively, magnetically sensitiveparticles can be embedded into the surface of a formed polishing pad inany suitable pattern or gradient, followed by heating the material ofthe deformable polishing pad body to its flow temperature, with theoptional application of pressure, to incorporate the particles into thematerial. Other methods for the non-uniform distribution of particles inthe deformable polishing pad body will be readily apparent to those ofordinary skill in the art.

The polishing pad of the invention can be configured as a top-pad or asubpad. In many polishing processes, the top-pad is the polishing padthat actually makes contact with the surface of the substrate beingpolished. Thus, the top-pad comprises a polishing surface. The subpadunderlies and supports the top-pad. When configured as a top pad, thepolishing pad of the invention is typically used in conjunction with asubpad. Alternatively, when configured as a top pad, the polishing padof the invention is typically used in conjunction with a subpad.

The invention also encompasses a polishing pad configured as a top padin combination with a subpad, wherein either or both the subpad or toppad can comprise the magnetically sensitive particles. In accordancewith this aspect of the invention, the top pad and subpad can beprovided by different layers of a single polymer sheet, or by separatepolymer sheets associated or bonded together. When the top pad andsubpad are provided by separate polymer sheets, the top pad polymersheet and subpad polymer sheet desirably are associated without the useof an adhesive (e.g., without an intervening adhesive layer). Forexample, the top-pad sheet and subpad sheet can be joined by welding(e.g., ultrasonic welding), thermal bonding, radiation-activatedbonding, lamination, or coextrusion. Alternatively, the top pad andsubpad can be provided by different layers or parts of a single polymersheet. For instance, a single-layer polymer sheet can by subjected to aprocess that alters the physical properties of one or both faces of thesingle-layer polymer sheet to provide a two-layer polymer sheet, whereinone layer serves as the top-pad and the other layer serves as thesubpad. For example, a solid polymer sheet can be selectively foamedsuch that porosity is introduced into one face of the polymer sheet,resulting in a two-layer polymer sheet (e.g., two-layer polishing pad)having a porous layer that is attached to a solid layer without the useof an adhesive. One of the layers provides the top pad, and the otherprovides the subpad. One or both layers of the polishing pad cancomprise the magnetically sensitive particles. According to any of theabove configurations, the subpad is preferably provided by a porouslayer comprising the magnetically sensitive particles.

When configured as a top-pad/subpad combination, or as a one-piecepolishing pad, the polishing pad of the invention can further comprise apolishing surface. The polishing surface can be provided by a separatelayer of material adhered or welded to the surface of the deformablepolishing pad body, or it can be provided by a surface of the deformablepolishing pad body. When the polishing surface is provided by a separatelayer of material, it can be adhered or welded to a surface of thedeformable polishing pad body by any suitable method, such as by way offriction (e.g., no intervening layer), hook-loop type interlockingfabrics, vacuum, magnetic forces, various adhesive compounds and tapes,“welding” the layers using chemicals, heat, and/or pressure, or othervarious methods. Typically, an intermediate backing layer such as apolyethyleneterephthalate film is disposed between the polishing layerand the subpad. This configuration of the polishing pad of the inventioncan, optionally, be used in conjunction with a subpad.

Whether provided by a surface of the deformable polishing pad body, orby a separate layer of material, the polishing surface can comprise anysuitable material, such as one or more of any of the polymers previouslyidentified with respect to the deformable polishing pad body. Thematerial can be the same as or different from the material of thedeformable polishing pad body. Typically, the polishing surfacecomprises a non-porous polyurethane.

The polishing surface can further comprise grooves, channels, and/orperforations, which facilitate the lateral transport of polishingcompositions across the surface of the polishing pad. Such grooves,channels, or perforations can be in any suitable pattern and can haveany suitable depth and width. The polishing surface can have two or moredifferent groove patterns, such as a combination of large grooves andsmall grooves as described in U.S. Pat. No. 5,489,233. Examples ofsuitable groove patterns include slanted grooves, concentric grooves,spiral or circular grooves, and XY crosshatch patterns, which can becontinuous or non-continuous in connectivity. Preferably, the polishingsurface comprises at least small grooves produced by standardpad-conditioning methods.

The polishing surface can be free of magnetically sensitive particles,or can comprise magnetically sensitive particles in any suitable amount.The concentration and distribution of magnetically sensitive particlesin the polishing surface can be configured in the same manner previouslydescribed with respect to the deformable polishing pad body. In a givenpolishing pad according to the invention, the concentration anddistribution of magnetically sensitive particles in the polishingsurface can be the same as or different from that of the deformablepolishing pad body.

When the polishing surface comprises magnetically sensitive particles,the particles are preferably coated to prevent any particles that becomeexposed during polishing from scratching the surface of the substrate.Alternatively, the magnetically sensitive particles used in thepolishing surface can be made of a material that will not scratch thesurface of a substrate being polished, such as non-abrasivemetal-organic or organic particles. Whether a given type of non-abrasiveparticle is abrasive or non-abrasive must be determined with respect tothe particular type of substrate being polished. The magneticallysensitive particles will typically be positioned in the polishing padsuch that they do not protrude from the surface of the polishing padduring polishing. However, the magnetically sensitive particles can bepositioned in the polishing pad such that they do protrude from thesurface in order to provide an abrasive polishing surface. When in thepresence of a magnetic field, the magnetically sensitive particlesprotruding from the surface of the polishing pad serve the dual purposesof providing a fixed abrasive in the polishing pad and providing for thealteration of the properties of the polishing pad as described herein.

The polishing pad of the invention can be configured for use inconjunction with an in situ polishing endpoint detection system. In situendpoint detection generally involves analyzing the surface of asubstrate during polishing through the use of light or other form ofradiation, so as to determine the end-point of the polishing process.Desirably, the polishing pad of the invention comprises a port oraperture that provides a path through which light or other form ofradiation can travel to reach the substrate surface. The port oraperture can be provided by a hole formed through the thickness of thedeformable polishing pad body, polishing surface, subpad, and any otherlayer which the polishing pad comprises. Alternatively, the polishingpad can comprise a “window” of a suitable polymer or other material thatis translucent or transparent to the light or other radiation used inthe detection technique. The particular type of port or aperture usedwill depend upon the specific endpoint detection technique chosen andthe type of radiation employed for that purpose. Techniques forinspecting and monitoring the polishing process by analyzing light orother radiation reflected from a surface of the workpiece are known inthe art. Such methods are described, for example, in U.S. Pat. No.5,196,353, U.S. Pat. No. 5,433,651, U.S. Pat. No. 5,609,511, U.S. Pat.No. 5,643,046, U.S. Pat. No. 5,658,183, U.S. Pat. No. 5,730,642, U.S.Pat. No. 5,838,447, U.S. Pat. No. 5,872,633, U.S. Pat. No. 5,893,796,U.S. Pat. No. 5,949,927, and U.S. Pat. No. 5,964,643.

When a magnetic field is applied to the polishing pad comprising thedeformable polishing pad body, one or more properties of the deformablepolishing pad body (or the polishing pad comprising the deformablepolishing pad body) are altered, desirably to a degree sufficient toaffect the polishing performance of the polishing pad. The propertiesthat are altered can be any of the properties of the polishing pad,including the storage modulus, compressibility, resilience, andhardness. Preferred configurations of the polishing pad comprise adeformable polishing pad body comprising magnetically sensitiveparticles in an amount such that, when in the presence of an appliedmagnetic field of about 1-1000 Gauss (e.g., about 5-500 Gauss, about10-250 Guass, or about 50-200 Gauss), one or more of these propertiesare changed by about 5% or more (e.g., about 10% or more), such as about15% or more (e.g., about 20% or more), or even about 25% or more (e.g.,about 30% or more) as compared to the polishing pad in the absence ofthe applied magnetic field.

The polishing pad of the invention can also comprise other polishing padelements such as stiffening layers, additional subpads, adhesive layers,backing materials, and other typical components.

The invention further provides a polishing system comprising (a) apolishing pad comprising a deformable polishing pad body andmagnetically sensitive particles dispersed therein, wherein one or moreproperties of the polishing pad are altered when in the presence of anapplied magnetic field, and (b) an adjustable-strength magnetic fieldpositioned proximate to the polishing pad. The polishing pad of thepolishing system is as described above with respect to the polishing padof the invention.

The adjustable-strength magnetic field can be provided by any suitableapparatus, such as a magnet or an electromagnet. The term“adjustable-strength” as used herein encompasses variable-strengthmagnetic fields (e.g., variable on a continuum of strengths) as well asmultiple-strength magnetic fields (e.g., having multiple fixed-strengthsettings). When the adjustable strength magnetic field is provided by amagnetic field having multiple fixed-strength settings, it is preferredthat the magnetic field has more than two strength settings (e.g., morethan an “on” and “off” setting) to allow greater flexibility in alteringthe properties of the polishing pad. The strength of the field can beadjusted, for example, by increasing or decreasing the amount of powersupplied, or by shielding the polishing pad from the magnetic field to agreater or lesser degree. The adjustable-strength feature of themagnetic field allows a user of the polishing system to change thestrength of the magnetic field and, thereby, control the properties ofthe polishing pad during use. As the magnetic field strength isincreased, the force exerted by the magnetically sensitive particles onthe deformable polishing pad body is increased, and the properties ofthe polishing pad comprising the deformable polishing pad body arealtered to a greater degree. Similarly, as the magnetic field strengthis reduced, the properties of the polishing pad are altered to a lesserdegree.

The adjustable-strength magnetic field is positioned proximate to thepolishing pad. For the purposes of this invention, theadjustable-strength magnetic field is considered to be “proximate” tothe polishing pad if the adjustable strength magnetic field is closeenough to the polishing pad to alter one or more properties of thepolishing pad. The adjustable strength magnetic field can be oriented inany suitable position relative to the polishing pad. For the purposes ofthe present invention, the magnetic field is considered to have lines offorce parallel to the direction of attraction and repulsion of themagnetic field. Typically, the magnetic field is positioned such thatthe lines of force are substantially perpendicular to the polishingsurface of the polishing pad. Alternatively, the magnetic field can bepositioned such that the lines of force are at an angle to the polishingsurface of the polishing pad, or even substantially parallel to thepolishing surface of the polishing pad. Also, the source of the magneticfield (e.g., the magnet or electromagnet) can be positioned relative tothe polishing pad and the substrate being polished such that thesubstrate is between the source of the magnetic field and the polishingpad, or, preferably, such that the polishing pad is between the sourceof the magnetic field and the substrate.

The adjustable strength magnetic field should be capable of providingsufficient magnetic force to alter one or more properties of thepolishing pad. The amount of force required for this purpose will dependupon the particular configuration of the polishing pad used in a givenapplication. Generally, an adjustable strength magnetic field capable ofgenerating about 1-1000 Gauss (e.g., about 5-500 Gauss, about 10-250Gauss, or about 50-200 Gauss) or more will be sufficient.

The strength of the magnetic field can be manually controlled (e.g.,operator-controlled). When manual controls are used, the appliedmagnetic field is typically adjusted by an operator to achieve ormaintain desired polishing parameters (e.g., removal rate, friction,roughness, dishing, etc.), or at the beginning or end of a polishingstage or a pre-determined time interval. For example, an operatormonitoring the material removal rate during polishing can adjust thestrength of the magnetic field to change or maintain a given materialremoval rate. Alternatively, or in addition to manual controls, thestrength of the magnetic field can be automatically controlled, forexample, through the use of a microprocessor. Automated controls can beused to automatically adjust the magnetic field strength according to apre-programmed set of instructions, or in response to changes inpolishing parameters. For example, the magnetic field can beautomatically adjusted in response to changes in polishing conditions byincorporating into the polishing system a feedback mechanism, wherebymonitors detect a change in one or more polishing conditions and delivera signal to the automated controls to adjust the magnetic fieldappropriately.

The invention also provides a method of polishing a substrate comprising(a) providing a polishing pad comprising a deformable polishing pad bodyand magnetically sensitive particles dispersed therein, wherein one ormore properties of the polishing pad are altered when in the presence ofan applied magnetic field, (b) contacting the polishing pad with asubstrate, (c) applying an adjustable-strength magnetic field to thepolishing pad to alter one or more properties of the polishing pad, and(d) moving the polishing pad relative to the substrate, therebypolishing the substrate. The polishing pad and adjustable-strengthmagnetic field are as described herein with respect to the polishing padand polishing system of the invention.

The method of the invention can further comprise adjusting theadjustable-strength magnetic field during polishing. The magnetic fieldcan be adjusted manually, or via automated controls, as discussed abovewith respect to the polishing system of the invention. The magneticfield preferably is adjusted so as to achieve a desired polishingproperty, such as to reduce over-polishing or reduce dishing of thesubstrate (e.g., improve planarity and within-die uniformity).

The polishing pad and polishing system of the invention is particularlysuited for use in conjunction with a chemical-mechanical polishing (CMP)apparatus. Typically, the apparatus comprises (a) a platen, which, whenin use, is in motion and has a velocity that results from orbital,linear, or circular motion, (b) a polishing pad of the invention incontact with the platen and moving with the platen when in motion, and(c) a carrier that holds a workpiece to be polished by contacting andmoving relative to the surface of the polishing pad. The polishing ofthe workpiece takes place by the workpiece being placed in contact withthe polishing pad and then the polishing pad moving relative to theworkpiece, typically with a polishing composition therebetween, so as toabrade at least a portion of the workpiece to polish the workpiece. Thepolishing composition typically comprises a liquid carrier (e.g., anaqueous carrier), a pH adjustor, and optionally an abrasive. Dependingon the type of workpiece being polished, the polishing compositionoptionally may further comprise oxidizing agents, organic acids,complexing agents, pH buffers, surfactants, corrosion inhibitors,anti-foaming agents, and the like. The CMP apparatus can be any suitableCMP apparatus, many of which are known in the art. The polishing pad andpolishing system of the invention also can be used with linear polishingtools.

The polishing pad, polishing system, and polishing method of theinvention is suitable for use in a method of polishing many types ofworkpieces (e.g., substrates or wafers) and workpiece materials. Forexample, the polishing pads can be used to polish workpieces includingmemory storage devices, glass substrates, memory or rigid disks, metals(e.g., noble metals), magnetic heads, inter-layer dielectric (ILD)layers, polymeric films, low and high dielectric constant films,ferroelectrics, micro-electro-mechanical systems (MEMS), semiconductorwafers, field emission displays, and other microelectronic substrates,especially microelectronic substrates comprising insulating layers(e.g., silicon oxide, silicon nitride, or low dielectric materials)and/or metal-containing layers (e.g., copper, tantalum, tungsten,aluminum, nickel, titanium, platinum, ruthenium, rhodium, iridium,alloys thereof, and mixtures thereof). In addition, the workpiece cancomprise, consist essentially of, or consist of any suitable metalcomposite. Suitable metal composites include, for example, metalnitrides (e.g., tantalum nitride, titanium nitride, and tungstennitride), metal carbides (e.g., silicon carbide and tungsten carbide),nickel-phosphorus, alumino-borosilicate, borosilicate glass,phosphosilicate glass (PSG), borophosphosilicate glass (BPSG),silicon/germanium alloys, and silicon/germanium/carbon alloys. Theworkpiece can also comprise, consist essentially of, or consist of anysuitable semiconductor base material. Suitable semiconductor basematerials include single-crystal silicon, poly-crystalline silicon,amorphous silicon, silicon-on-insulator, and gallium arsenide.

EXAMPLE

The following example illustrates the preparation and use of a polishingpad, polishing system, and polishing method according to the invention.

A polishing pad comprising a deformable polishing pad body andmagnetically sensitive particles dispersed therein is fabricated byblending polyurethane foam particles and magnetite (Fe₃O₄) at atemperature above the flow temperature of the polyurethane. The mixtureis cast into a disc-shaped polishing pad.

The polishing pad is mounted on the platen of a CMP polishing machine asa subpad beneath a standard polyurethane top pad, and a patternedsubstrate is positioned on the polishing tool of the polishing machinein contact with the surface of the top pad. A variable-powerelectromagnet is positioned such that the polishing pad is between theelectromagnet and the substrate, and the lines of force of the magneticfield are perpendicular to the surface of the polishing pad. Thepolishing process is started, and a polishing composition is supplied tothe surface of the polishing pad and substrate. The electromagnet is inthe “off” position. After several minutes, dishing in the surface of thesubstrate is detected, and the electromagnet is turned on at low power.The application of the magnetic field causes the subpad to compressagainst the platen, reducing the compressibility of the subpad.Polishing is continued for several more minutes, after which time thedishing in the substrate is reduced, but still evident. The strength ofthe electromagnet is increased, thereby causing the subpad to furthercompress against the platen, and polishing is continued with furtherreduction in the dishing of the substrate.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1-30. (canceled)
 31. A polishing system comprising (a) a polishing padcomprising a deformable polishing pad body and magnetically sensitiveparticles dispersed therein, wherein one or more properties of thepolishing pad are altered when in the presence of an applied magneticfield, and (b) an adjustable-strength magnetic field positionedproximate to the polishing pad.
 32. The polishing system of claim 31,wherein the strength of the magnetic field is manually controlled. 33.The polishing system of claim 31, wherein the strength of the magneticfield is automatically controlled.
 34. The polishing system of claim 33,wherein the strength of the magnetic field automatically adjusts inresponse to changes in polishing conditions.
 35. The polishing system ofclaim 33, wherein the strength of the magnetic field automaticallyadjusts according to a pre-set program.
 36. The polishing system ofclaim 31, wherein the one or more properties of the polishing pad thatare altered in the presence of an applied magnetic field are one or moreproperties selected from the group consisting of the storage modulus,compressibility, percent-rebound, and hardness of the polishing pad. 37.A method of polishing a substrate comprising (a) providing a polishingpad comprising a deformable polishing pad body and magneticallysensitive particles dispersed therein, wherein one or more properties ofthe polishing pad are altered when in the presence of an appliedmagnetic field, (b) contacting the polishing pad with a substrate, (c)applying a magnetic field to the polishing pad to alter one or moreproperties of the polishing pad, and (d) moving the polishing padrelative to the substrate, thereby polishing the substrate.
 38. Themethod of claim 37, further comprising adjusting the strength of themagnetic field during polishing, thereby altering one or more propertiesof the polishing pad.
 39. The method of claim 37, wherein the strengthof the magnetic field is adjusted in response to a change in polishingconditions.
 40. The method of claim 38, wherein the strength of themagnetic field is adjusted according to a pre-set program.
 41. Themethod of claim 38, wherein adjusting the strength of the magnetic fieldreduces over-polishing dishing in the substrate.
 42. The method of claim37, wherein the one or more properties of the polishing pad that arealtered in the presence of an applied magnetic field axe one or moreproperties selected from the group consisting of the storage modulus,compressibility, resilience, and hardness of the polishing pad.
 43. Thepolishing system of claim 31, wherein the polishing pad has a storagemodulus of about 100 to about 1000 MPa in the absence of an appliedmagnetic field.
 44. The polishing system of claim 31, wherein thepolishing pad has an average percent compressibility, under a load ofabout 32 kPa, of about 2% or more in the absence of an applied magneticfield.
 45. The polishing system of claim 31, wherein the polishing padhas an average percent-rebound, after application of a load of about 32kPa, of about 25% or more in the absence of an applied magnetic field.46. The polishing system of claim 31, wherein the polishing pad has aShore Durometer hardness of about 40 A to about 90 D in the absence ofan applied magnetic field.
 47. The polishing system of claim 31, whereinthe deformable polishing pad body comprises a polymer.
 48. The polishingsystem of claim 47, wherein the polymer is selected from the groupconsisting of elastomers, polyurethanes, polyolefins, polycarbonates,polyvinylalcohols, nylons, natural and synthetic rubbers, styrenicpolymers, polyaromatics, fluoropolymers, polyimides, cross-linkedpolyurethanes, thermoset polyurethanes, cross-linked polyolefins,polyethers, polyesters, polyacrylates, elastomeric polyethylenes,copolymers and block copolymers thereof, and mixtures and blendsthereof.
 49. The polishing system of claim 48, wherein the deformablepolishing pad body comprises a foam polymer.
 50. The polishing system ofclaim 49, wherein the foam comprises predominantly open cells.
 51. Thepolishing system of claim 49, wherein the foam comprises predominantlyclosed cells.
 52. The polishing system of claim 49, wherein the foamcomprises a mixture of open and closed cells.
 53. The polishing systemof claim 31, wherein the magnetically sensitive particles have anaverage particle diameter of about 5 μm or less.
 54. The polishingsystem of claim 31, wherein the magnetically sensitive particles areinorganic particles.
 55. The polishing system of claim 54, wherein themagnetically sensitive particles are selected from the group consistingof Fe₃O₄, Nd—Fe—B, Ba—Sr ferrite, Ni—Zn—Cu ferrite, SmCo₅, Sm₂Co₁₇,iron, steel, and mixtures thereof.
 56. The polishing system of claim 54,wherein the magnetically sensitive particles are coated.
 57. Thepolishing system of claim 31, wherein the magnetically sensitiveparticles are organic or metal-organic particles.
 58. The polishingsystem of claim 57, wherein the magnetically sensitive particles areselected from the group consisting of V[tetracyanoethylene]_(˜2),V[Cr(CN)]_(˜0.9), Cr(tetracyanoethylene)₂, KV[Cr(CN)₆], and C-60fullerene.
 59. The polishing system of claim 31, wherein themagnetically sensitive particles are distributed uniformly throughoutthe deformable polishing pad body.
 60. The polishing system of claim 31,wherein the magnetically sensitive particles are distributed throughoutthe deformable polishing pad body in a non-uniform manner.
 61. Thepolishing system of claim 31, wherein the magnetically sensitiveparticles are distributed throughout the deformable polishing pad bodyaccording to a gradient.
 62. The polishing system of claim 31, whereinthe magnetically sensitive particles are distributed in selected areasof the pad.
 63. The polishing system of claim 31 further comprising apolishing surface.
 64. The polishing system of claim 63, wherein thepolishing surface is provided by a surface of the deformable polishingpad body.
 65. The polishing system of claim 63, wherein the polishingsurface is provided by a separate layer.
 66. The polishing system ofclaim 63, wherein the polishing surface comprises magnetically sensitiveparticles.
 67. The polishing system of claim 66, wherein themagnetically sensitive particles are coated particles.
 68. The polishingsystem of claim 66, wherein the magnetically sensitive particles areorganic particles or metal-organic.
 69. The polishing system of claim63, wherein the polishing surface is free of magnetically sensitiveparticles.
 70. The polishing system of claim 31, further comprising anendpoint detection port.